The present invention relates to a copying method which is capable of selecting a positive-to-positive image or a negative-to-positive image as desired without changing the polarity of a developer or a charger. More particularly, the invention relates to an image forming method using an intermediate recording medium which permits free selection of a negative image or a positive image of an original by selectively setting a voltage applied.
Among the conventional copying methods adapted to produce a positive-to-positive image or a negative-to-positive image a process is known which is carried out by preparing two different types of positive and negative developers and changing the transfer polarity at each transfer step. Another known process is effected by preparing a sensitive medium of joined P-type and N-type semiconductors or a sensitive medium composed of a semiconductor of one conductivity type and a transparent dielectric joined thereto or a bipolar sensitive medium and switching the charging polarity to positive or negative to execute positive development or reversal development using only one type of developer thereby obtaining a negative-to-positive image or a positive-to-positive image as desired. In the first-mentioned process, however, there exists a disadvantage of requiring two devices while the second-mentioned process has problems regarding the points of the change in polarity, positive and negative charging characteristics, image quality, production cost and so forth. Therefore, neither of the above-described processes has found application on a wide-scale industrial basis.
In the specification of Japanese Patent Application No. 41303/1978 filed by the instant applicant there is disclosed a copying machine which employs an intermediate recording medium to form an image on its specular and diffusive regions and reads out the image by optically selecting a specular reflection pattern or a diffusive reflection pattern from which is produced a negative or positive image. In this machine, there is a great difference in the quantity of light between the specular reflection pattern and the diffusive reflection pattern so that, in case a single light source is used for reading out the pattern, it becomes necessary to reduce the quantity of the specular reflection light by use of a neutral density filter or a diaphragm for equalizing the quantity of specular reflection light to the quantity of the diffusive reflection light. Because of the presence of the filter, a considerable loss of the light is unavoidable. If no neutral density filter or diaphragm is used, some voltage switching means is required to change the quantity of light in two steps. Consequently, the above machine does not provide a large quantity of light in all circumstances and has the difficulty of forming an image on a medium of low-sensitivity material.